Bryan A. Baum1

Ping Yang2, Andrew Heymsfield3

1 NASA Langley Research Center, Hampton, VA 2 Texas A&M University, College Station, TX 3 National Center for Atmospheric Research, Boulder, CO

Goal: Provide ice cloud bulk scattering models that are developed consistently for suite of multispectral and hyperspectral instruments

Hyperspectral/Multispectral Ice Cloud Microphysical and Optical Models

Hyperspectral/Multispectral Ice Cloud Microphysical and Optical Models

5th Workshop on Hyperspectral Science June 7-9, 2005

Bulk Scattering ModelsBulk Scattering Models

Operational satellite-based cloud retrievals require the ability to simulate realistic ice cloud radiances quickly

Simulations require bulk scattering parameters such as

single-scattering albedoscattering phase function or asymmetry factorextinction efficiency or scattering/absorption cross sections

Scattering parameters in turn are based on the

cloud phase (ice, water, or mixed)particle size distributionparticle habit distributionwavelength(s)

Have libraries of scattering properties from Ping Yang & colleagues

Library of SWIR to Far-IR Scattering Properties100 to 3250 cm-1

Library of SWIR to Far-IR Scattering Properties100 to 3250 cm-1

Library of ice particle scattering properties include

Hexagonal platesSolid and hollow columnsAggregatesDroxtals3D bullet rosettes

45 size bins ranging from 2 to 9500 m

Spectral range: 100 to 3250 cm-1 at 1-cm-1 resolution

Properties for each habit/size bin include volume, projected area, maximum dimension, single-scattering albedo, asymmetry factor,and extinction efficiency

* Yang, P., H. Wei, H. L Huang, B. A. Baum, Y. X. Hu, M. I. Mishchenko, and Q. Fu, Scattering and absorption property database of various nonspherical ice particles in the infrared and far-infrared spectral region. In press, Applied Optics.

Particle Size Distributions Particle Size Distributions

Gamma size distribution* has the form:

N(D) = NoDe-D

where D = max diameter

No = intercept

= dispersion

= slope

The intercept, slope, and dispersion values are derived for each PSD by matching three moments (specifically, the 1st, 2nd, and 6th moments)

Note: when = 0, the PSD reduces to an exponential distribution

*Heymsfield et al., Observations and parameterizations of particle size distributions in deep tropical cirrus and stratiform precipitating clouds: Results from in situ observations in TRMM field campaigns. J. Atmos. Sci., 59, 3457-3491, 2002.

Field Campaign InformationField Campaign Information

Field Campaign

Location Instruments Number of PSDs

FIRE-1 (1986) Madison, WI 2D-C, 2D-P 246

FIRE-II (1991) Coffeyville, KS Replicator 22

ARM-IOP (2000) Lamont, OK 2D-C, 2D-P, CPI 390

TRMM KWAJEX (1999)

Kwajalein, Marshall Islands

2D-C, HVPS, CPI 418

CRYSTAL-FACE (2002)

Off coast of Nicaragua

2D-C, VIPS 41

Probe size ranges are: 2D-C, 40-1000 m; 2D-P, 200-6400 m; HVPS (High Volume Precipitation Spectrometer), 200–6100 m; CPI (Cloud Particle Imager), 20-2000 m; Replicator, 10-800 m; VIPS (Video Ice Particle Sampler): 20-200 m.

Replicator Ice Crystal Profiles from FIRE Cirrus II CampaignReplicator Ice Crystal Profiles from FIRE Cirrus II Campaign

Ice Crystal Profiles From Tropical CirrusIce Crystal Profiles From Tropical Cirrus

Particle Size DistributionsFrom Gamma Fits

Particle Size DistributionsFrom Gamma Fits

Midlatitude cirrus characteristics

• Size sorting more pronounced

• Small crystals at cloud top

• More often find pristine particles

Tropical cirrus anvil characteristics

Form in an environment having much higher vertical velocities

• Size sorting is not as well pronounced

• Large crystals often present at cloud top

• Crystals may approach cm in size.

• Habits tend to be more complex

• Note that CRYSTAL distributions tend to be the narrowest overall

Ice Particle Habit DistributionIce Particle Habit Distribution

At this point, we have- ice particle scattering library- wealth of microphysical data for ice clouds (1117 PSDs)

Next issue: develop a ice particle habit distribution that makes sense

Note: each idealized ice particle has a prescribed volume, and hence mass

Compare IWC and Dm computed from integrating over the habit and size distributions to those values estimated from techniques developed by Heymsfield and colleagues from analyses of their in situ data

Ice Water Content and Median Mass Diameter Ice Water Content and Median Mass Diameter

Guidelines

4 size domains defined by particle maximum length

Droxtals: used only for smallest particles

Aggregates: only for particles > 1000 m

Plates: used only for particles of intermediate size

Ice Particle Habit Percentages Based on Comparison of Calculated to In-situ Dm and IWC

Ice Particle Habit Percentages Based on Comparison of Calculated to In-situ Dm and IWC

Proposed ice particlehabit mixture

Max length < 60 m100% droxtals 60 m < Max length < 1000 m 15% bullet rosettes 35% hexagonal plates 50% solid columns 1000 m < Max length < 2500 m45% solid columns45% hollow columns10% aggregates

Max length > 2500 m97% bullet rosettes 3% aggregates

Relationship Between Dm and DeffRelationship Between Dm and Deff

Relationship Between IWC and DeffRelationship Between IWC and Deff

Small Particle Sensitivity StudySmall Particle Sensitivity Study

Note that CRYSTAL distributions tend to be the narrowest overall

For all 41 CRYSTAL size distributions, increase the number of particles with Dmax < 20 m by a factor of 100 or 1000

For building look-up tables for operational retrievals, want discrete set of models that are evenly spaced in effective diameter

Development of Discrete Set of ModelsDevelopment of Discrete Set of Models

Bulk Scattering ModelsAvailable for Multiple Instruments

Bulk Scattering ModelsAvailable for Multiple Instruments

Provide bulk properties (mean and std. dev.) evenly spaced in Deff from 10 to 180 m for

asymmetry factor phase function

single-scattering albedo extinction efficiency & cross sections

IWC Dm

Models available at http://www.ssec.wisc.edu/~baum for

IR Spectral Models (100 to 3250 cm-1)

MODIS AVHRR AATSR MISR

VIRS MAS (MODIS Airborne Simulator)

ABI (Advanced Baseline Imager) POLDER (Polarization)

SEVIRI (Spinning Enhanced Visible InfraRed Imager)